Chain or DAG? Underlying data structures, architectures, topologies and consensus in distributed ledger technology: A review, taxonomy and research issues

Abstract

Since the advent of blockchain in 2009, it has drawn considerable attention from academia and industry. Later, the notion of Distributed Ledger Technology (DLT) extended the conception of blockchain, which covered both chain-based and Directed Acyclic Graph (DAG)-based immutable databases maintained by multiple participants. A large number of data structures have been proposed in DLTs to meet different applications requirements. This paper presents a survey of different structures designs in DLTs, including chain-based and DAG-based structures. During the reviewing, we also briefly investigate how the structure could affect system functions to solve the application problems and inspire readers to build a connection of the motivations and structure designs. Our contributions include the following: (i) classify and discuss recent, relevant work from the perspective of system structures. (ii) investigate different DLT structures and the motivations of utilising these structures, and analyse corresponding algorithms combined with the structures if possible. (iii) analyse security properties and potential attacks to different structures (iv) point out current challenges and propose future directions of structures and corresponding algorithms in DLT.